This invention relates to a method for controlling a two-stroke internal-combustion engine with fuel injection in the low load range in which the supply of fuel to the combustion space is interrupted or released as a functional operating parameters.
A two-stroke internal-combustion engine with fuel injection is known from German Patent Document DE-OS 37 35 595 in which the supply of fuel to the combustion space in the partial-load range is permitted or prevented by a valve as a function of operating parameters.
In addition, a method for operating a two-stroke internal-combustion engine with an electronically controlled direct fuel injection is known from German Patent Document DE-OS 39 11 016, in which case the fuel injection during idling and in the low partial-load range takes place intermittently.
Finally, a method for interrupting the fuel supply is known from German Patent Document DE-PS 36 27 471. A characteristic diagram which is a function of operating parameters is used for this purpose, whereby an incomplete combustion is to be avoided of a cylinder filling which is not ignitable.
A disadvantage of the above-mentioned methods is that the interruption of the fuel supply is started for fixed specified operating conditions and is maintained in each case for a fixed specified period. In this case, it is not taken into account that the residual gas content in the combustion space which is decisive for the capability to ignite as well as the distribution of the residual gas in the combustion space may assume different values for each engine because of manufacturing tolerances, as well as that the residual gas content will change in the course of the engine operation, for example, as a result of deposits in the inlet and outlet, of wear-caused leakages in the inlet and outlet system, and of a wear-caused change of the friction device pressure. Finally, in the case of the known methods, the influence is also not taken into account which is exercised on the ignition reliability by the wear, the manufacturing tolerance and the contamination.
Although, in the case of the known methods, these unreliable factors can be offset to a certain degree by the fact that the number of working strokes without fuel injection is increased to such an extent that sufficient oxygen will be available in the combustion space under all operating conditions and thus the injected fuel is burnt reliably. However, under normal conditions, the ignition frequency of the engine and as a result the smooth running and the driving comfort would therefore be reduced. Inversely, the number of working strokes without fuel injection could be selected to be very low. However, the probability would then be increased that the injected fuel is not burnt which, in turn, would lead to an increase of the fuel consumption and a deterioration of the HC-emissions.
It is an object of the invention to provide a method for controlling two-stroke internal-combustion engines in the low load range in which the number of working strokes without fuel supply is continuously adapted to the actual condition of the engine so that an optimal compromise is achieved between a smooth running, the emissions and the fuel consumption.
According to the invention, this object is achieved by providing a method for controlling a two-stroke internal-combustion engine with fuel injection in the low load range, in which the supply of fuel to the combustion space is interrupted or released as a function of operating parameters, wherein
for each injection operation, the number of working strokes (f.sub.required) for which the fuel injection is to be interrupted is read out from a characteristic diagram (F) which is a function of operating parameters,
the fuel supply is interrupted for (f.sub.required) working strokes,
after the (f.sub.required) working strokes without fuel injection have been carried out, the capability of the working gas to ignite is checked, and
the characteristic diagram (F) is adaptively corrected as a function of the capability of the working gas to ignite.
The method according to the invention has the advantage that the number of the working strokes at which the fuel supply is interrupted is adapted continuously. This means that the fuel supply is interrupted until the residual gas situated in the combustion space has been displaced by fresh air to such an extent that the injected fuel can actually be burnt. This avoids or at least reduces misfires and therefore improves the engine pollutant emission.
Further advantages and details of the method according to the invention are found in the subclaims and the specification.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.